Problem: Simplify the following expression: $k = \dfrac{a + 7}{6a + 3} + \dfrac{-9a - 9}{6a + 3}$
Explanation: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{a + 7 - 9a - 9}{6a + 3}$ Combine like terms: $k = \dfrac{-8a - 2}{6a + 3}$